Iraqi officials say unidentified gunmen have shot and killed a senior aide to radical Shi'ite cleric Moqtada al-Sadr in the southern holy city of Najaf Friday.
Police and the director of the Sadr movement's office in Najaf confirmed the killing. The officials say Riyadh al-Nouri was driving home from Friday prayers when he was shot.
Authorities in Najaf have imposed a curfew. Sadr's spokesman in Najaf, Salah al-Obeidi, says Sadr calls on his supporters to remain calm. The aide also quoted Sadr as blaming "occupying forces" and those working with them for the killing.
U.S. officials have not responded to the allegation, but in Washington, U.S. Defense Secretary Robert Gates told reporters he doubts Sadr would be subject to arrest by U.S. forces.
Gates said the Shi'ite cleric is a significant political figure and that the United States wants him to work within the Iraqi political process.
Sadr has not been seen in public since May of last year.
Separately, Iraqi security officials said a suicide bomber killed three policemen and wounded five others today near Ramadi in Anbar province.
In Baghdad, a mortar apparently aimed at the U.S.-protected Green Zone fell short, blasting into the area of the Palestine Hotel. Iraqi police say three civilians were killed.
Coalition forces in Iraq have killed 12 suspected insurgents in air strikes in the southern city of Basra today and in Baghdad's Sadr City district late Thursday.
Fighting has intensified in Iraq since Iraqi Prime Minister Nouri al-Maliki ordered a crackdown on Shi'ite militias last month.
Some information for this report was provided by AFP, AP and Reuters.